The present invention relates to a multiple-access communication system, such as a bidirectional CATV network, a passive optical star network and so forth for a center station to dynamically assign upstream bandwidth to subscriber stations, and in particular relates to a method of guaranteeing quality of service in the upstream channel.
A communication system, such as a bidirectional CATV network or a passive optical star network, generally has a broadcasting downstream channel from a center station to subscriber stations, and a time-division multiple-access upstream channel from subscriber stations to the center station. In a communication system like this, the center station assigns one or more identifiers to the subscriber station when a subscriber station begins an operation, and then the subscriber station transmits data to the center station. Procedures of upstream bandwidth allocation are detailed below.
First, the center station transmits reservation-permit information to the subscriber stations, and then the subscriber stations having an upstream data to transmit send reservation information comprising an identifier and a requested upstream bandwidth to the center station. If reservation information sent from multiple subscriber stations collides in the upstream channel, the center and subscriber stations resolve the collision so that the center station eventually receives all the reservation information correctly.
Also, when a subscriber station holds next data to send at time of data transmission, it transmits the current data with appending reservation information for the next data. The center station makes upstream-bandwidth-grant information from this reservation information and send it to the subscriber station, and the subscriber station sends the upstream data to the center station in the allocated upstream bandwidth. If the subscriber stations do not particularly require a service quality, the center station performs above-mentioned upstream bandwidth allocation procedure equally to all subscriber stations for each upstream data transmission.
Accordingly, when the upstream channel is congested in a communication system like this, collision of reservation information among subscriber stations and retention of reservation information in the center station may increase, resulting in an increase in a delay time required for upstream bandwidth allocation.
On the other hand, when a required upstream service quality such as guaranteed bandwidth or upper limit of transmission delay is already known, the quality of services in the upstream channel must be guaranteed. Examples of such services are real-time audio and video packet transmission.
Conventionally, as a first method to guarantee a service quality in a multiple-access communication system like this, there is one in which a subscriber station informs the center station of a required service quality before sending an upstream reservation information, and the center station, allocates upstream bandwidth at a periodic basis. As a second method to guarantee a service quality in a multiple-access communication system like this, there is one in which the center station periodically sends reservation-permit information to the subscriber station to allocate upstream bandwidth on priority basis to the subscriber station. As an example of reports about the first method of the prior art, there is James E. Dail et al., xe2x80x9cIEEE Communication Magazine,xe2x80x9d pp. 104-112, March 1996. Also, as an example of reports about the second method of the prior art, Patent Application H10-18318 can be mentioned.
In case of the first method to guarantee service quality of the prior art, if a quantity of upstream data generated by a subscriber station temporarily exceeds an upstream bandwidth periodically allocated by the center station, the subscriber station may send reservation information in a normal procedure to request excess bandwidth and the center station receiving this allocates the excess upstream bandwidth if there is still some available.
Also, in case of the second method to guarantee service quality of the prior art, if a quantity of upstream data generated by a subscriber station temporarily exceeds the guaranteed upstream bandwidth, the subscriber station may request excess upstream bandwidth in response to the periodic reservation-permit information from the center station, and the center station receiving this allocates the excess upstream bandwidth if there is still some available.
Like this, in the method to guarantee service quality of the prior art in above-mentioned communication system, when the subscriber station attempts to send upstream data at a transmission rate higher than the guaranteed upstream rate, the center station has no means to defer upstream bandwidth allocation. Accordingly, if a certain subscriber station sends upstream data at a rate far above a guaranteed upstream rate, upstream bandwidth allocation to other subscriber stations is delayed due to the lack of limiting upstream bandwidth allocation to the guaranteed rate, resulting in a degradation of service quality supplied to other subscriber stations.
Further, in a method to guarantee service quality of the prior art, the time required for queuing-reservation information at the center station cannot be guaranteed. Particularly, when the center station periodically sends reservation-permit information to subscriber stations by the conventional method, the time between the reception of reservation information and the upstream bandwidth allocation at the center station is not bounded. Accordingly, there is a problem that the service quality cannot be guaranteed if queuing delay at the center station becomes long.
It is therefore an object of the present invention, in a multiple-access communication system, such as a bidirectional CATV network, a passive optical star network and so forth where a center station dynamically allocates bandwidths of an upstream channel to subscriber stations, to measure and guarantee a service quality supplied for each service permitted to subscriber stations and prevent a degradation in service quality for other subscriber stations due to an influence of a subscriber station that sends data exceeding a previously contracted guaranteed value of a service quality.
Other objects of the present invention will become clear as the description proceeds.
A multiple-access communication system of a first invention wherein the center station has means for permitting the use of services of different qualities which it guarantees to subscriber stations; means for assigning identifiers corresponding to each service to the subscriber stations; means for transmitting reservation-permit information to the subscriber stations; means for receiving reservation information from the subscriber stations; means for measuring an upstream service quality being supplied with regard to a service corresponding to an identifier that is added to a reservation information when receiving the reservation information from a subscriber station; means for comparing the measured upstream service quality with a guaranteed value of a previously assigned service quality; means for immediately accepting the reservation information, if the measured value is below the guaranteed value, and assigning an upstream bandwidth; and means for accepting a reservation information of other subscriber stations prior to accepting the received reservation information, if the measured value is above the guaranteed-value, so as to prevent degradation of service quality to the other subscriber stations.
Also, wherein a subscriber station has means for requesting the use of services to the center station; means for receiving identifiers assigned by the center station according to each requested services; means for receiving a reservation-permit information from the center station; means for transmitting a reservation information to the center station in an upstream bandwidth designated by the reservation-permit information; means for adding an identifier corresponding to a service type of an upstream data to be sent to the reservation information; means for receiving an upstream-bandwidth-grant information from the center station; and means for transmitting the upstream data to the center station in the upstream bandwidth designated by the upstream-bandwidth-grant information.
A multiple-access communication system of a second invention, as claimed in the first invention, wherein the center station has means for holding a scheduled allocation time information determined from a guaranteed service quality and an guaranteed upstream bandwidth and for holding a permissible fluctuation quantity information of an allocation time when a current allocation time is earlier than a scheduled allocation time, for each service the center station permitted to subscriber stations; means for comparing a current allocation time with a scheduled allocation time when the center station receives a reservation information from a subscriber station; means for immediately accepting a reservation information if the current allocation time is later than the scheduled allocation time, or if the current allocation time is earlier than the scheduled allocation time but later than a time adding a permissible fluctuation quantity of the allocation time to the scheduled allocation time; and means for accepting a reservation information of other subscriber stations prior to accepting the received reservation information, so as to prevent degradation of a service quality to the other subscriber stations, if the current allocation time is earlier than the time adding the permissible fluctuation quantity of the allocation time to the scheduled allocation time.
A multiple-access communication system of a third invention as claimed in the second inventions wherein supposing that an upstream rate guaranteed to a subscriber station is g bits/sec, a permissible fluctuation quantity of an allocation time is Tb seconds and a requested upstream bandwidth of a reservation information which the center station received from the subscriber station is B bits, the center station has means for immediately accepting a reservation information and updating a scheduled allocation time to a value adding (B/g) seconds to a current allocation time if the current allocation time is later than the scheduled allocation time, or for immediately accepting the reservation information and updating the scheduled allocation time to a value adding (B/g) seconds to the scheduled allocation time if the current allocation time is earlier than the scheduled allocation time but later than a time adding Tb to the scheduled allocation time, and further, for accepting a reservation information of other subscriber stations prior to accepting the received reservation information, if the current allocation time is earlier than the time adding Tb to the scheduled allocation time, so as to prevent degradation of service quality to the other subscriber station.
A multiple-access communication system of a fourth invention, as claimed in the first invention, wherein the center station has means for holding statistical values of an upstream service quality measured in the past for each service permitted to subscriber stations; means for updating, when measuring an upstream service quality, a statistical value of the upstream service quality from statistical values of the upstream service quality measured in the past and temporary values of the upstream service quality measured up to the present after updating a previous statistical value; means for immediately accepting a reservation information and assigning an upstream bandwidth if the statistical value of the upstream service quality is below a guaranteed value of a previously assigned service quality when receiving an upstream reservation information; and means for accepting a reservation information of another subscriber station prior to accepting the received reservation information, so as to prevent degradation of service quality to the other subscriber stations, if the statistical value of the upstream service quality exceeds the guaranteed value of service quality.
A multiple-access communication system of a fifth invention as claimed in the fourth invention, supposing that an interval of measuring an upstream service quality being supplied by the center station for each service is Ti seconds, an upstream rate guaranteed to a subscriber station is g bits/sec, a statistical value of an average upstream rate for an upstream service is m bits/sec, a temporary upstream rate up to the present after updating a previous statistical value is r bits/sec, and a weighting average index is w, w being values between 0 and 1, means for updating a value of the statistical value m of upstream rate to w*r+(1xe2x88x92w)*m when the center station measures the upstream service quality; means for immediately accepting a reservation information and assigning an upstream bandwidth if m is below g when receiving an upstream reservation information; and means for accepting a reservation information of other subscriber stations prior to accepting the received reservation information if m is above g, so as to prevent degradation of service quality to the other subscriber stations.
A multiple-access communication system of a sixth invention as claimed in the first, second, third, fourth or fifth invention, wherein the center station and a subscriber station have means for dividing an upstream bandwidth into slots of ten and some bytes and up to some ten bytes; and means for making reservation of and allocating an upstream bandwidth in a unit of said slot.
A multiple-access communication system of a seventh invention, as claimed in the first, second, third, fourth, fifth or sixth invention, wherein the center station has means for assigning a priority for each service permitted to subscriber stations; queues for temporarily holding reservation information received for each priority; means for inserting a reservation information to the tail of a queue of a priority corresponding to an identifier appended to a reservation information when receiving the reservation information; means for removing a reservation information from the head of a queue of a highest priority when allocating an upstream bandwidth; means for comparing a measured value of a service quality corresponding to an identifier of the removed reservation information with a guaranteed value of a previously assigned service quality; means for immediately accepting a reservation and allocating an upstream bandwidth if the measured value is below the guaranteed value; and means for inserting a reservation information to the tail of a queue of a lower priority, if the measured value is above the guaranteed value, so as to prevent degradation of service quality to otter subscriber stations.
A multiple-access communication system of an eighth invention as claimed in the seventh invention, wherein the center station has means for holding the sum of requested upstream bandwidths contained in each reservation information for a queue of each priority; means for receiving a reservation information from subscriber stations; means for adding an requested upstream bandwidth contained in the received reservation information to the current sum of requested upstream bandwidth; means for inserting the received reservation information to a queue corresponding to a priority if the result is below a previously set upper limit of the sum of requested upstream bandwidth which each queue can hold; and means for inserting the received reservation information to a queue of a lower priority if the result exceeds the upper limit.
In a multiple-access communication system of a first invention, first of all, when a subscriber station requests a guarantee for quality of an upstream services it sends a service-quality-request information of each service to a center station. This service-quality-request information contains a peak rate, average rate, maximum burst length, maximum delay and so forth of traffic. When the center station can offer the service quality requested from the subscriber station, it assigns an identifier to the subscriber station. Also in the center station, a guaranteed service quality and a measured value of an upstream service quality being supplied are controlled for each service permitted to the subscriber station.
When the subscriber station send an upstream data, first, when receiving a reservation-permit information from the center station, the subscriber station sends a reservation information made up of an identifier corresponding to a service for the upstream data and a requested upstream bandwidth to the center station. The center station, upon receiving the reservation information from the subscriber station, compares a guaranteed upstream service quality corresponding to the identifier contained in the reservation information and a measured value of an upstream service quality being offered. After comparing, if the measured value of the service quality is below the guaranteed value, the center station immediately accept the reservation information and allocates an upstream bandwidth, or if the measured value is above the guaranteed value, the center station accepts a reservation information from other subscriber stations prior to accepting the received reservation information.
Thus, it is possible to prevent a degradation in service quality for other subscriber stations due to an influence of a subscriber station that sends data exceeding a transmission rate or burst length of a previously assigned guaranteed value of a service quality.
In a multiple-access communication system of a second invention as claimed in the multiple-access communication system of the first invention, the center station holds, for each service it permitted to subscriber stations, a scheduled allocation time information determined from a guaranteed service quality and an allocated upstream bandwidth, and a permissible fluctuation quantity information of an allocation time when a current allocation time is earlier than a scheduled allocation time.
The center station, upon receiving said reservation information from the subscriber station, compares the scheduled allocation time of a service corresponding to an identifier appended to the reservation information and the current allocation time. After comparing, if the current allocation time is later than the scheduled allocation time, or if the current allocation time is earlier than the scheduled allocation time but later than a time adding a permissible fluctuation quantity of the allocation time to the scheduled allocation time, the center station immediately accepts the reservation information. On the other hand, if the current allocation time is earlier than the time adding the permissible fluctuation quantity of the allocation time to the scheduled allocation time, the center station accepts a reservation information of other subscriber stations prior to accepting the received reservation information.
Like this, at the-center station, whether or not a subscriber station is sending an upstream data exceeding a previously assigned guaranteed service quality can easily be controlled by comparing a scheduled allocation time of an upstream bandwidth for each service with a current allocation time.
In a multiple-access communication system of a third invention as claimed in the multiple-access communication system of the second invention, supposing that an upstream rate which the center station guarantees a subscriber station is g bits/sec, a permissible fluctuation quantity of an allocation time is Tb seconds and a requested upstream bandwidth of a reservation information which the center station receives from the subscriber station is B bit, if the current allocation time is later than the scheduled allocation time, the center station immediately accepts the reservation information and updates the scheduled allocation time to a value adding (B/g) seconds to the current allocation time. If the current allocation time is earlier than the scheduled allocation time but later than a time adding Tb to the scheduled allocation time, the center station immediately accepts the reservation information and updates the scheduled allocation time to a value adding (B/g) seconds to the scheduled allocation time. Further, if the current allocation time is earlier than the time adding Tb to the scheduled allocation time, the center station accepts a reservation information of other subscriber stations prior to accepting the received reservation information.
Like this, by the center station deciding updating of a scheduled allocation time and a method of accepting reservation information by comparing a current allocation time with the scheduled allocation time, it is possible to immediately accept a reservation information while a subscriber station is performing transmission within a guaranteed upstream rate or by temporarily exceeding the upstream rate, and if the subscriber station continuously exceeds a guaranteed upstream rate, it is possible to accept a reservation information of other subscriber stations prior to accepting the received reservation information.
In a multiple-access communication system of a fourth invention as claimed in the multiple-access communication system of the first invention, the center station holds a statistical value of an upstream service quality measured in the past for each service permitted to subscriber stations. When measuring an upstream service quality being supplied to a subscriber station, the center station takes a weighting average of statistical values of the service quality and temporary values of service quality measured up to the present after updating a previous statistical value and updates the statistical value of the upstream service quality.
The center station, if the statistical value of service quality is below a guaranteed value of a previously assigned service quality when receiving an upstream reservation information, immediately accepts the reservation information and allocates an upstream bandwidth, and if the statistical value exceeds the guaranteed value of service quality, the center station accepts a reservation information of other subscriber stations prior to the received reservation information, so as to prevent degradation of service quality to the other subscriber stations.
Like this, by taking statistics of a measured upstream service quality, it is possible to guarantee an upstream service quality without immediately delaying acceptance of a reservation even when the upstream service quality frequently exceeds a guaranteed value due to sudden fluctuations in traffic.
In a multiple-access communication system of a fifth invention as claimed in the multiple-access communication system of the fourth invention, it is supposed that an interval of measuring a service quality being supplied by the center station for each service is Ti seconds, an upstream rate guaranteed to said subscriber station is g bits/sec, a statistical value of an average upstream rate for an upstream service is m bits/sec, a temporary upstream rate up to the present after updating a previous statistical value is r bits/sec, and a weighting average index is w, w being values between 0 and 1. The center station, when measuring an upstream service quality, updates a value of the statistical value m of upstream rate to w*r+(1xe2x88x92w)*m. If m is below g when receiving an upstream reservation information, the center station immediately accepts the reservation information and allocates an upstream bandwidth, and if m is above g, the center station accepts reservation information of other subscriber stations prior to the received reservation information, so as to prevent degradation of service quality to the other subscriber stations.
Like this, by taking statistics of an average upstream rate for an upstream service via a weighted average, it is possible to guarantee an upstream service quality without immediately delaying acceptance of a reservation even when the upstream service quality frequently exceeds a guaranteed value due to sudden fluctuations in traffic.
In a multiple-access communication system of a sixth invention as claimed in the multiple-access communication system of the fifth invention, the center station and a subscriber station divide an upstream channel into slots of ten and some bytes and up to some ten bytes, make reservation and allocate upstream bandwidth in a unit of slot. Like this, by dividing an upstream channel in a slot unit, it is possible to easily assign an upstream bandwidth and measure an upstream service quality.
In a multiple-access communication system of a seventh invention as claimed in the multiple-access communication system of the first, second, third, fourth, fifth or sixth invention, the center station assigns an identifier and a priority for each service it permitted to subscriber stations. The center station internally manages a service quality guaranteed for each service, a priority of service and an upstream service quality being offered. The center station has queues to temporarily hold reservation information received for each priority, and, when receiving a reservation information from a subscriber station, the center station inserts a reservation information to the tail of a queue of a priority corresponding to an identifier appended to the reservation information.
The center station, when assigning an upstream bandwidth, removes a reservation information from the head of a queue of a highest priority. The center station measures a service quality being offered corresponding to an identifier of the removed reservation information and compares the measured service quality with a value of a previously assigned guaranteed service quality. If the measured value is below the guaranteed value, the center station immediately accepts the reservation and allocates an upstream bandwidth, and if the measured value is above the guaranteed value, the center station inserts the reservation information to the tail of a queue of a lower priority
Like this, by the center station having a queue corresponding to a priority for temporarily holding a reservation information, it is possible to accept a reservation of other subscriber stations prior to accepting a reservation information of a subscriber station that sends an upstream data exceeding a service quality, so as to prevent degradation of service quality to the other subscriber station.
In a multiple-access communication system of an eighth invention as claimed in the multiple-access communication system of the seventh invention, the center station holds the sum of requested upstream bandwidth contained in each reservation information for a queue of each priority. The center station, receiving a reservation information from a subscriber station, adds a requested upstream bandwidth contained in the received reservation information to the current sum of requested upstream bandwidth. If the result is below a previously set upper limit of the sum of requested upstream bandwidths which the queue can hold, the center station inserts the received reservation information to a queue corresponding to a priority, and if the result exceeds the upper limit, the center station inserts it to a queue of a lower priority.
Like this, by holding the sum of requested upstream bandwidth of reservation information contained in a queue of each priority and by inserting a reservation information to a queue via comparison with a previously set upper limit, it is possible to guarantee an upper limit of a delay time required for queuing for each priority.